The motor actions of natural neurokinins and their specific agonists on the gastrointestinal tract of the rat.

Neurokinins (NK) are a group of peptides that share a common C-terminal and play an important role in control of the motor functions of the mammalian gut. Neurokinin receptors such as NK1, NK2 are certainly present in any segment of gut, whereas the NK3 receptors are probably present in the ileum of the Guinea pig and duodenum of the rat. We measured gastrointestinal responses with natural NK and their very specific agonists to determine the probable receptors in the stomach and small intestine of Sprague-Dawley rats. After overnight fasting, the rats were intubated with a catheter to feed saline liquid meal that contained 10% charcoal. Simultaneously, various doses of NK ranged selected from 10(-10) and 10(-7) mol kg-1 included substance P (SP), neurokinin A (NKA), neurokinin B (NKB), septide, [Nle10]-NKA4-10, senktide, and vehicle were intraperitoneally injected. At 15 min after being fed test meal, the rats were sacrificed. Then we removed entire gut including the stomach to measure the total length of small intestine and transit length of the charcoal, from which the transit ratio was calculated. In comparison with ratios of rats treated with vehicle, the inhibited transit ratios for charcoal were seen among SP at 10(-10) mol kg-1, NKA at 10(-10) and 10(-7) mol kg-1, [Nle10]-NKA4-10 at 10(-7) mol kg-1, and senktide at all doses except 10(-8) mol kg-1. Enhanced transit ratios were seen for septide at the doses 10(-8) and 10(-7) mol kg-1. Likewise the mean total intestinal lengths of rats if they received various treatments of peptides except that rats treated with NKB had somewhat diminished length than those of vehicle-treated rats. Some natural NK and their very specific receptor agonists mainly inhibited rat gastrointestinal charcoal transits. We suggest the probable presence of NK1, NK2 and NK3 receptors in the small intestine and stomach including pylorus of the rat.